The present invention relates to a semiconductor sensor incorporating a diaphragm formed on a semiconductor substrate, and more particularly, to an improvement of an electrical connection configuration for increasing the manufacturing productivity for the semiconductor sensor.
Recently, progress in Micro Electro Mechanical System (MEMS) technology for forming a mechanical component (movable component) and an electrical component on a semiconductor substrate has resulted in development of a microscopic semiconductor sensor incorporating a diaphragm formed on a semiconductor substrate. A diaphragm type semiconductor sensor has been applied to acoustic sensors, pressure sensors, acceleration sensors, and etc.
An example of diaphragm type acoustic sensor is an electrostatic capacity sensing semiconductor microphone described in Japanese Laid-Open Patent Publication No. 60-500841. The electrostatic capacity sensing semiconductor microphone includes a diaphragm electrode, which vibrates in accordance with the sound pressure, and a fixed electrode, which is fixed to the semiconductor substrate. The diaphragm electrode is arranged facing towards the fixed electrode. Vibrations of the diaphragm electrode change the distance between the two electrodes. The change in the distance between the electrodes changes the electrostatic capacity of a capacitor formed by the two electrodes. The electrostatic capacity sensing semiconductor microphone outputs a detected signal in accordance with the voltage change resulting from the change in electrostatic capacity.
Japanese National Phase Patent Publication No. 2004-537182 describes a package for protecting a semiconductor substrate (sensor chip) on which a diaphragm type semiconductor sensor is formed. In the package, the sensor chip is adhered and coupled to a printed wiring board with an IC chip on which a control integrated circuit for the sensor is formed. The surface of the printed wiring board is covered with a cover. The diaphragm is exposed from the sensor chip. Thus, the MEMS configuration of the diaphragm and the like is normally formed in the surface of the semiconductor substrate located opposite to the side to which the printed wiring board is adhered. Thus, in the prior art, the IC chip or the wiring of the printed wiring board is wire bonded to the sensor chip in the package.
To perform wire bonding, a bonding electrode pad must be formed on both surfaces of the printed wiring board and the sensor chip. The electrode pad increases the area for the printed wiring board and the sensor chip and enlarges the package module of the semiconductor sensor.
In wire bonding, a manufacturing defect may be caused due to ultrasonic vibrations generated when connecting wires to the bonding electrode pad. A normal semiconductor device that does not have a MEMS configuration has a rigid bulk structure in which there is substantially no gaps, fine linear portions, and thin portions. Thus, such a semiconductor device has a relatively high resistance with respect to ultrasonic vibration. Comparatively, a semiconductor sensor incorporating movable components such as a diaphragm often includes gaps, fine liner portions, and thin portions. Thus, there is a tendency for manufacturing defects to be caused by ultrasonic vibrations. Particularly, in a microphone for detecting sound, the rigidity of the diaphragm cannot be significantly increased since sensitivity must be increased. Thus, a microphone is more likely to be affected by ultrasonic vibrations than other types of diaphragm semiconductor sensors, such as a pressure sensor, an acceleration sensor, and the like.
Wire bonding increases the manufacturing cost. Generally, gold or aluminum is used for the bonding electrode pad. In a semiconductor device that does not include a MEMS configuration, aluminum, which is relatively inexpensive, is often used as the material for the bonding pad. However, in a semiconductor sensor including a MEMS configuration, a sacrifice layer must be removed with hydrofluoric acid to form movable components. Thus, aluminum must have high solubility with respect to hydrofluoric acid. As a result, gold, which is more expensive, must be used. This increases the manufacturing cost.